Overvoltage protectors are widely used for the protection of equipment from overvoltage conditions which may be caused by lightning, contact with high voltage lines, or miscellaneous transient conditions.
One type of overvoltage protector is a five pin protector module for telephone circuits; an example is disclosed in Kidd et al., U.S. Pat. No. 4,958,254.
Another type of overvoltage protector is a gas tube type. An environmentally protected gas tube overvoltage protector is disclosed in Napiorkowski, U.S. Pat. No. 4,212,047. Napiorkowski's gas tube protector is potted in an epoxy potting compound. Because the potting compound may interfere with the air gap or the short circuiting clip in Napiorkowski's gas tube protector, the assembly is wrapped and voids filled with PTFE or equivalent material prior to the potting.
Napirokowski's epoxy potting compound is not entirely satisfactory, however, due to the fact that potting compound expands differently from the surrounding enclosure during changes in temperature, over time causing cracks to appear in the potting compound which lessen its environmental protection of the protector.
Two gas tube type station protectors having a base opening and two upstanding line terminals projecting through terminal openings are the TII 355 and the AT&T 325EW. The TII 355 station protector module employs environmental protection by potting the entire base opening area and its two line terminal openings. The AT&T 325EW station protector employs an O-ring for its two line terminal openings.
Gels are used in other types of prior art electrical devices. See, for example, gel sealed apparatus as disclosed in U.S. Pat. Nos. 4,212,047; 4,600,261; 4,634,207; 4,741,709; 4,824,390; 4,846,721; 5,102,347; 5,140,746; and 5,195,125.
In order to perform their intended function, overvoltage protectors, however, must be capable of changing from a first state, allowing normal current to proceed through the protector, to a second state during overvoltage conditions, usually causing a short circuit to protect electrical components from excessive voltage and resultant damage. The protectors may change to the second state by the operation of coil, cantilever, or other type springs which urge a grounded component of some type through an air gap into contact with a component in electrical connection with the normal circuit. It is clear that the preservation of air gaps and operability of the moving parts is critical to the intended operation of these protectors. Perhaps for this reason, the prior art has apparently not provided gel-sealed overvoltage protectors.